Drying apparatus



Dec 2, 1924.

J. B. WELCH DRYING APPARATUS 1922 2 Sheets-Sheet 1 b mxmwn Filed July $2 .J. B. WELCH DRYING APPARATUS Filed July 1922 2 Sheets-Sheet 2 JOHN-B. WELCH, or snnavnroa'r, nomsmna harms .arranarcs.

. Application filed July 19, 1922. Serial No. 575,955.

To all whom it may concern:

Be it known thatl, JOHN. B. WELCH, a citizen of the United States, residing in Shreveport, in the parish of Caddo and State of Louisiana, have invented an improvement in Drying Apparatus, of which 'the following description, in connection with the accompanying drawings, is a specification, like characters'fon the drawings representing like parts.

This invention relates to apparatus for drying lumber and other materials.

The object of the invention is to provide drying apparatus of novel and improved construction adapted to dry the material in a superior manner under drying conditions which are practically self-regulating, thus insuring the most desirable drying results.

To this end, one feature of the invention contemplates a construction of drying apparatus having provision for the development of a self-controlled recirculation of air actuated primarily by differences in density of the air. Another feature of the invention contemplates the withdrawal of a portion of the hot humid air from the wet end of the dryer and the distribution of this hot humid air to the dry end of the dryer for controlling .the air conditions at both the wet and dry ends of the dryer. This is preferably accomplished by the provision of a throat injector in a distributing duct for the positive induction of wet air from the green end and dellvery of it to the dry end of the dryer. The withdrawal of the wet air may and preferably will be accomplished by the cold inrushing fresh air or by means of differences in vapor pressures, and in both cases the distribution of the hot moist air from the wet end to the dry end will be selfregulating to maintain the desired air conditions within the dryer.

Other features of the invention will be hereinafter described and particularly pointed out in the claims.

In the drawings the invention is illustrated as embodied in a progressive kiln. tor lumber-drying,.wherein Fig. 1 is a vertical section with a portion broken away, showing the elongated kiln Figs. 2 and 3 are details in side and end elevation, respectively, of a portion of the distributing duct by which hot moist air from the wet end of the kiln is distributed to the dry end of the kiln; Fig. l is a sectional plan of a portion of the kiln shown in Fig. 1; Fig. 5 is a cross-section on line 55 of Fig. 4; and Fig. 6 is a detail to be referred to.

In drying lumber and other material, the

more modern practice contemplates the initial heating of the green material throughout in an atmosphere of sufficiently high humidity to accomplish the heating without evaporation of appreciable moisture from the green material. After the material has thus been heated thoroughly to a sufficiently high temperature, the material is brought into contact with air of gradually decreasing humidity, thereby permitting gradual evaporation of the moisture and preventing surface drying, cracking and other disadvantages. In drying lumber on a large scale progressive kilns are usually employed whichcomprise elongated chambers otten'ot a length approximating 100 to- 120 feet. During the operation of the kiln, the lumber is progressively moved from the entrance or wet end of the kiln to the dry or delivery end of the, kiln. Provision is made for maintaining the temperature and 30 humidity conditions within the kiln such that the entering of green lumber is initially brought into contact with air of relatively high humidity and at a temperature such that the moisture within and throughout the body of the lumber is raised sutiiciently in H temperature to provide for the proper amount of evaporation and without evaporation of appreciable quantities thereof. The

lumber is thereafter progressively movedto the dry or delivery end of the kiln, and in the course of its movement it encounters air of progressively decreasing humidity, so that the moisture is caused to gradually evaporate in a manner such as to avoid surface drying, cracking and similar difiiculties.

The success or" the operation of such kilns has heretofore depended to a large extent upon the care with which. the humidity and temperature conditions within the different portions of the kilns have been controlled by the operator, and particularly at the dry end thereof. Automatic humidity controllers for injecting moist air by means of steam sprays into the kiln have been employed. These attempts, however, to assist in controllin the humidity conditions within the hi n have generally resulted in the stoppage of circulation within the kiln,

the excessive use of live steam thus adding considerably to the cost of operation; and furthermore, because the addition of moistill also been KUJ some l1 T A ture in the the I by of biot c e stelletioe oi SllCii. e; y c the J is huh,

In certain other types of progressive kilns, the fresh eir'is 0 1m itted directly uni der the dry end of the um er without being heated and Without the addition of moisture. This subjects the lumber at the dry end to cold dry eir thus immediately lowering the humiidityat this end to a dangerous point such as to incur liability of injury to the lumber. The addition of moisture by means of sprays to raise the humidity of the air et'this end results, however, in raising the humidlty at the green end of the kiln,

thus precticelly terminating the drying entirely at the green end with the result thet in such kilns practically all of the drying is caused to take piece et the dry end, and the edventeges of pro ressive drying ere lost,

These various oisedysuteges iii prior types and constructions of dr iii epperstus he self-conere avoided in accordance with invention by the developh trolled TQCllLClllmlI-lflfl sir c by did ferences in of the e r, in the pr ferred form of drying apparatus, one or more b y-passes humid sir tus to the the hot hi1 plished b. Wet end of h e wet sphere end thereof. l/vithdrawal .d elr oreiferebly ,oco""- e through which.

the fresh a to to withdrew the hot humid r end to deliver it dr end of the kiln, With this o it won oi zipper :us in which recirculetiou is d veloped by diii ereiices in densities the pefitielly counterbelei columns of hot end cold air, the dos humidity Gt'illfill tioes at the end as well at thd hot end are cohtrolle l B l o eti memier so that the I tie lumber through defective of the G131 eretort carelessness, inmmentio-u, or other Wise, is eliminated,

ilhese verious disadvantages in prior and constructions oi. eppereprovided bypassing hoto oied, accordance with i on, b development 01 .c .o current eir fro wot one othe difyer through e bydry nd thereoi'. Durihg the ope oi the ii upon at erticulztr h l e of humid eir t i I 3 1 the bypass mey an pr be regulated so as to produci "ying conditions in the kiln, J the differences in sir pressure or ve'por pressure as the efi'ectivo moons N1 causing movement of the hot humid through the bypass, the volume of he sir withdrew is caused to very with yet tions in the yspor pressures at the dry of the kiln, so that in this manner deiici i. cies in. humidity at the dry end ere imme dietely and automatically compensated -for in an exceedingly simple and yet highly efli drying which comprises, in geneml, an elongated dirying chamber 10, prefembly oiE co crete or other insulating materiel having t usuel openings 12, 314E, at opposite en thereof for the entrance end delivery lumber be dried, Suiteble doors of 16, 18, are provided for closing" such 0 inc,

Eli lumber is introduced in the usu i manner through the opening 12, m moved progressively toward the dry end of the hilii upon suitable tracks 20, shown in F Fresh air is delivered at the end oi the chamber 19 through ducts l c'eted etthe bottom portion of the dryer extended the Wet end thereof, as shown it Fig i, l and 5. Th fresh air emerges from top or upper surface of the ducts through suitable slits or openings W iere it i 5S througrh the lumber at dr end of the dryer.,' Provision is made- 1 spreyiug live steam into the drying che 1-= her at both the dry cud Wet ends in provide the requisite host and huuii y ruling the diying operstion, ose spray nozzles 28 end 30, i c iii 34%, as, are positioned at d SW6d oints, shown in Figs. 1, 4; e11 f 1: lines ere provided with the o y'al 38, so that both the ty him the, kiln at the humidi W1 1,517.,eas

thereof may be controlled by the operator.

.erably will be provided with the usual heatingcoils or piping 21 extending beneath the tracks 20 (see Fig. 1) and along the entire length of the chamber andjby which the heat necessary for the maintenance of the desired temperatures and the final drying-out of the lumber may be obtained.

In order to provide positive internal circulationof air from the dry to the. wet end of the kiln, and in order that deficiencies or variations in the air conditions at the dry end thereof may be automatically compensated for and the desired air conditions maintained, distributing-ducts 40 are provided at the wet end of the kiln, at opposite side walls thereof, and extended downwardly and iriwardly, terminating iff'the'fresh air ducts 24 as shown. During the operation of the kiln upon any particular kind of lumber, the valves 38 controlling the steam sprays are adjusted to produce the desired humidity and temperature conditions within.

the kiln. Fresh air enters through the fresh air ducts 24 from the outside atmosphere with a strong rush because of the difl'erences in vapor pressures due to the differences in temperatures at the opposite ends of the ducts 24, the temperature at the dry end usually approximating 200 F. As the fresh air rushes past the ends of the distributing ducts 40, the aspirating effect operates to withdraw some of the hot humid air from the wet end ofthe kiln, and to cause it to be delivered along with the fresh air through the slits or openings 26, and into the dry end of the kiln. The continued withdrawal of the air-from the wet end during the operation of the kiln assists in producing a definite positive air movement from the dry to the wet end, a fact which is of immense importance for the most successful drying of the lumber. After the-kiln is initially adj usted for operation upon a particular class of lumber, humid air of a definite volume and at a definite rate will be withdraw from the wet end and delivered to the dry end.-

Ihis initial adjustment together withthe volume of fresh air introduced mayv be conveniently made by dampers 44, 46, hinged to partitions 48, 50, in the fresh air' ducts 24, as shown. These dampers will preferably be arranged to be operated from without the kiln by suitable rods and connections not shown. When variations occur in the air conditions at the dry end of the kiln, corresponding variations in vapor pressures at the ends of the'ducts 24 will occur, and because of the fact that the movement of the air through the ducts 24 and also the withdrawal of the humid air from the wet end of the kiln through the distributing ducts 40 are primarily actuated by difierences in the densities of the columns of air at the wet and dry ends, it is apparent that when such variations occur they will be automatically compensated for, and the air conditions at both ends restored to normal in a positive, simple, self-regulating manner.

It will be observed that the cold inrushing fresh air as it is directed pastthe end of the distributing ducts 40 by the partitions 48, 50, performs an action similar to a throat injector. In order to increase the velocity of the air circulation through the portion of the ducts 24 beyond the distributing ducts 40, steam sprays 51 may and preferably will be provided therein, as illustrated in Fig. 4. If desired a throat injector of the form illustrated in detail in Fig. 6 may be employed, the cold air entering through the conduit 54 and the hot humid air being drawn through the surrounding. conduit 56. In order to increase the velocity of the air, steam injectors or sprays 58 are preferably employed, arranged as shownin Fig. '6.

It will also'be observed that the number and location of the conduits 40 through which the hot humid air is withdrawn may be varied to meet various conditions arising in practice, thus enabling air to be withdrawn from points 'of higher humidity and delivered to points of lower humidity.

During each. cycle of the air circulationthrough the kiln, a, portion of the humid air is drawn from the wet end upwardly through the exhaust fines 60 to the atmosphere. In this manner the excess moisture is continuously removed from the kiln.

While the invention has been illustrated and described as embodied in a progressive kiln for lumber drying, it will be understood that the invention may, with advantage, be embodied in apparatus for drying other material, within the scope of the following claims.

1. A dryingapparatus comprising an elongated drying chamber for containing the material to be dried, means for admitting fresh air to the dry end of the apparatus, means for producing predetermined within the apparatus, and means for developing self-controlledair recirculation actuated by differences in densities of partially counterbalancing columns of hot and cold air.

2. A drying apparatus comprising an elongated drying chamber, forv containing the material to be dried, means for admitting fresh air to the dry end of the apparatus, means for producing predetermined conditions of humidity and temperature within the apparatus, and means actuatedby differences in density of partially counterbalancing columns of hot and cold air for withdrawing humid air from the wet end of the apparatus and delivering it with the fresh air to the dry end.

3. A drying apparatus comprising an elongated drying chamber for containing the materal to be dried, means for admitting fresh air to the dry end of the apparatus, means for producing predetermined conditions of humidity and temperature within the apparatus, and means actuated by delivered to the dry end.

4. A drying apparatus comprising an elongated drying chamber for containing the material to be dried, means for admitting fresh air to the dry end of the apparatus, means for producing predetermined conditions of humidity and temperature within the apparatus, and means actuated by differences in density of partially counterbalancing columns of hot and cold air for adding heat to the fresh incoming air delivered to the dry end.

5. A drying apparatus comprising an elongated chamber, a conduit for admitting freshair to the apparatus, and means for connecting the fresh air conduit and wet end of the apparatus for withdrawing humid hot air and delivering it to the dry end of the apparatus along with the fresh air.

6.A drying apparatus comprising an elongated chamber, a conduit for admitting fresh air to the apparatus, and means for connecting the fresh air conduit and wet'end of the apparatus provided with a throat injector for positive induction of air from the wet end actuated by means of the velocity of incoming fresh air.

7. A drying apparatus comprising an elongated chamber, a conduit for admitting fresh air to the apparatus, and means for connecting the fresh air conduit and wet end of the apparatus for withdrawing humid hot air from a point of maximum air density in the wet end of the apparatus.

8. A drying apparatus comprising an elongated chamber, a conduit for admitting fresh air to the chamber, and means for connecting the fresh air conduit and wet end of the apparatus provided with a throat injector for the positive induction of air from a point of maximum air density in the wet end of the apparatus.

9. A drying apparatus comprising an elongated chamber, a conduit for admitting fresh air to the apparatus, and means for connecting the fresh air conduit and wet end of the apparatus forwithdrawing humid hot,

air from a point of high air density in the wet end of the apparatus.

10. A drying apparatus comprising a dry ing chamber, means for permlttin movement of the material to be drie theremamas through, means for causing air movement through the material in a direction counter-- current to the movement of said material, and means for Withdrawing air from the wet to the dry end of the apparatus operated and controlled by density difierences of the air, said means including a bypass conduit for bypassing air from arelatively humid to a relatively dryportion of the chamber,

11. A drying apparatus comprising a chamber for containing material to be dried, and self-regulating means for controlling the humidity within the chamber by the distribution of moistair from a point of higher to a point of lesser humidity.

12. A drying apparatus comprising a chamber, means for admitting fresh air to the chamber, and means for developing selfcontrolled air recirculation within the chamber comprising a throat injector cooperating with the chamber and the means for admitting the fresh air.

13. .A drying apparatus comprising a chamber for containing material tobe dried, a conduit for delivering fresh air to one portion of the chamber, connections between a portion of the chamber, in which the humidity is relatively high, and a fresh air conduit for withdrawing moist air and delivering it with the fresh air, and a steam spray in the conduit for increasing the velocit of air movement therein.

14. drying apparatus comprising a chamber for containing material to be dried,

a conduit for delivering fresh airto one portion of the chamber, connections between a portion of the chamber in which the humidity is relatively high and the fresh air conduit for withdrawing moist air and delivering it with the fresh air, and means in the conduit for increasing the velocity of air movement therein.

15. A drying apparatus comprising an elongated chamber through which the material to be dried is progressively passed, means for admitting fresh air to the chamher, and means for developing self-controlled recirculation of the airilongitudinally through the elongated chamber.

16. A drying apparatus comprising an elongated chamber through which the material to be dried is progressively passed, means for admitting fresh air to the chamber, and self-regulated means actuated by differences in the densities of partially counter-balancing currents of air for developin the circuluation of the air longitudinally of the elongated chamber.

lln testimony whereof, I have signed my name to this specification,

JUHN B. 'WELCH,

lltl 

